Red Lion LEGEND - Manual (Page 21)

PROGRAM COUNTER MODULE
In the Counter Module, the count mode, reset action, and automatic reset
capability are selected. The following flowchart shows only the Counter portion:
COUNT MODES (CNT.INPUT)
There are seven available count modes. User Input 4 programmed for the
count Inhibit function can be used with any count mode. Input A signal is used
for the count and rate input. Input B is used in combination with Input A for
C o u n t C o n t r o l D i r e c t i o n , Q u a d r a t u r e c o u n t i n g , A n t i - c o i n c i d e n c e
Add/Subtract or Anti-coincidence Add/Add counting applications.
CT+DIRX1 (X1 COUNTING WITH DIRECTION)
The unit counts one count on every negative edge of the input signal at
Input A. The direction of the count is determined by the logic state of Input B.
A high level at Input B causes the unit to count in a positive direction. A low
level causes the unit to count in a negative direction. The rate display is NOT
affected by the logic state of Input B.
CT+DIRX2 (X2 COUNTING WITH DIRECTION)
The unit counts one count on every negative edge of the input signal and
one count on every positive edge of the input signal at Input A. In this mode,
the input signal is effectively doubled. The direction of the count is
determined by the logic state of Input B. A high level at Input B causes the unit
to count in a positive direction. A low level causes the unit to count in a
negative direction. The rate display is NOT affected by the state of Input B.
QUAD X1 (QUADRATURE X1)
Quadrature counting modes are primarily used in positioning and
anti-jitter applications. This mode works due to the manner in which the two
incoming pulses are positioned relative to each other. The pulse signal on
Input B is shifted 90º away from the pulse signal at Input A. These two signals
are processed by the Legend Plus as follows:
Input A serves as the count and rate input, while Input B serves as the
quadrature input. For quadrature with single edge counting, the counter
counts in a positive direction when Input A is a negative going edge and Input
B is at a low level. The counter counts in a negative direction when Input A is
a positive going edge and Input B is at a low level. All transitions on Input A
are ignored when Input B is at a high level. These logic rules provide the basis
for anti-jitter operation which prevents false counts from occurring due to
back-lash, vibration, chatter, etc.
QUAD X2 (QUADRATURE X2)
When two edge counting is used, the quadrature mode works the same as
with single edge counting when Input B is low. But when Input B is a high
level, counts at Input A are no longer ignored. Instead, the logic rules for
Input A are complemented, allowing both edges of Input A to be counted.
This doubles the effective resolution of the encoded input.
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